Sonic treating apparatus



Dec. 4, 1962 J. P, @NEM 3,066,686 E soNc TREATING APPARATUS Filed Mayl0. 1960 t Po- 121-;

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.' SONIC ENERGY GENERATOR Unite i States 3,066,686 SONXC TREATINGAlPPARATU .lames P. ONeill, Playa Del Rey, Calif., assigner to TheBendix Corporation, North Hollywood, Calif., a corporation of DelawareFiled May 10, 1969, Ser. No., 28,031 Claims. (Sl. 134-122) Thisinvention relates to apparatus for treating material with sonic energyand, more particularly, to apparatus for sonic cleaning of continuousstrips of materials, such as sheets of glass or metal.

The utility of sonic energy for cleaning contaminants from the surfaceof a variety of articles is well recognized. Cleaning is accomplished byimmersing the article in a liquid medium, such as Water, and byintroducing sonic energy into the medium in such intensity thatcaviation occurs in the region of the article. The cavitation effect isassociated with the formation of gaseous bubbles Within the cleaningmedium upon intense pressure changes in a localized area. Cavitationtends to literally burst contaminants from the surface of the article tobe cleaned.

In one cleaning system particularly adapted to the cleaning of residualadhesive from one face of a sheet of glass, it is customary to pass theglass in nearly direct contact with an array of magnetostrictivetransducers arranged in a plane with a small amount of liquid confinedbetween the glass and the transducers. Cavitation is produced in theregion between the transducer faces and the glass as it moves past, andthe contaminant adhesive is removed. Cleaning systems of this type arecommonly referred to as contact systems since the transducer faces arepractically in contact with the Work piece.

One difliculty which has been encountered in contactcleaning apparatusis that the cavitation produced in the region of the transducers causeserosion of the transducers and requires frequent replacement of thetransducer faces.

ln another type of cleaning apparatus, a plurality of transducers arearranged in the walls of a cylindrical tank so that energy produced isfocused at a central region. This type of apparatus is particularlyuseful in the cleaning of small objects which are suspended within thetank in the region of the focus. The transducers are operated at a powerlevel low enough that cavitation does not occur at their faces, but onlyin the region of the focusing of energy from several transducers.However, such focused sonic energy cleaning systems have not beenadaptable to the cleaning of wide strips of material or to continuouscleaning operations because the active cleaning region is comparativelylocalized along the central axis of the tank.

With this state of the prior art in mind, it is a general object of theinvention to facilitate the sonic treatment of continuous stripmaterials.

A more specific object of the invention is to achieve high eiiciencycleaning of strip materials characteristics of the contact type cleaningapparatus along with the long transducer life characteristic of focusedtype cleaning apparatus.

Another object of the invention is to improve the efciency of soniccleaning by employing reinforcement of sonic energy by reflection fromselected portions of the cleaning apparatus.

These objects are all achieved in accordance with this invention, oneembodiment of which comprises a cleaning tank filled With liquid andincluding means for driving continuous strips of material through theupper portion of the tank. Within the tank is an enclosure in the formof a sector of a cylinder extending across the tank including convergingrigid Walls with horizontal slots of length sufficient to allow thepassage of the strip material through the enclosure, a closure at theconvergent end, and a cylindrically curved wall at the lower ordivergent end of the enclosure. A plurality of transducers are mountedin the lower curved wall with their radiating surfaces arranged ordirected toward a common focus at the axis of the cylindrically curvedWall. The slot openings in the side Walls are positioned a shortdistance below the liquid level Within the tank and are at a distancefrom the transducer faces which is determined in accordance with astanding Wave pattern established Within the internal enclosure When thetransducers are operating. The nature and position of the convergent endclosure are designed to utilize the effects of the standing Wave patternwithin the cleaning enclosure.

In one embodiment of the invention, the upper closure of the cleaningchamber is a thin metallic diaphragm positioned at a pressure node orpoint of maximum velocity gradient on the opposite side of stripmaterial passing through the slots from the transducers. The stripmaterial passing through the slots is positioned at a point of maximumpressure gradient or, in other words, a velocity node in the standingwave pattern. The thin metallic diaphragm, exposed on one side to theliquid medium within the internal enclosure and on the other side to thesurrounding air, provides a pressure-release reecting surface for sonicenergy from the transducers which has passed through the work piece.

ln another embodiment of the invention, the cleaning chamber is of thesame size and shape as in the irst embodiment; however, the convergentend has no closure and is exposed directly to the air. in thisembodiment there also is an impedance mismatch at the surface causingthe rellection of sonic energy back toward the Work piece.

In still another embodiment, the closure of the cleaning chamber at theconvergent end is a solid member which acts as a rigid reflector, andthat member is positioned directly above the work piece at a pressureantinode.

In each of these embodiments, the treating or cleaning action on theWork piece is enhanced iirst by the focusing effect of the arrangementof the transducers; second, by the restriction of the sonic energywithin the chamber by the rigid convergent side walls; and, third, bythe reflection of the energy to produce standing waves.

An advantage of the invention is that these enhanced cleaningcharacteristics are obtained in apparatus adapted to the treatment ofcontinuous strip material which heretofore has been successfully cleanedby sonic energy only in contact type apparatus. Another advantage of theinvention is that the transducers may be operated at an amplitudeinsuiiicient to produce cavitation at the faces of the transducers,thereby minimizing the wear on the transducer while, through thefocusing elfect, producing cavitation in the region of the work piece.

These advantages are all achieved in accordance with the invention, onefeature of which is the arrangement of converging boundary walls of thecleaning enclosure forming a segment of a cylinder with transducersmounted to radiate energy toward the axis of the cylinder and withopenings to pass continuous strip or sheet material through theenclosure.

Another' feature of this invention involves the positioning of the stripor sheet material guiding means so that it passes through a pressureanti-node region resulting from a standing wave pattern establishedwithin the cleaning enclosure.

Another feature of this invention resides in the use of a sonic energyreliector positioned beyond the work piece 4at a predetermined distancein order to produce standing waves and achieve reinforcement of thesonic energy in the region of the material to be cleaned.

A full understanding of the invention may be had from n the followingdetailed description with reference to the drawing in which:

FIG. 1 is a longitudinal, vertical sectional View of a cleaningapparatus employing this invention taken in the plane I-I of FIG. 2;

FIG. 2 is a transverse section through the apparatus of FIG. l takenalong the line 2-2 of FIG. l;

FIG. 3 is a fragmentary sectional view similar to FIG. l, showinganother embodiment of the invention; and

FIG. 4 is a fragmentary sectional view similar to FIG. l, showing stillanother embodiment of the invention.

Referring now to FIGS. 1 and 2, apparatus for the cleaning of strips ofsemirigid material includes a tank having sidewalls and bottom ofrelatively thin metal and including a curved lip 11 at one side overwhich a strip 13 to be cleaned enters the tank and a curved lip 12 atthe opposite side of the tank 10' where the strip 13 emerges. In thedrawing, the curvature of lips 11 and 12 is greatly exaggerated. Thestrip may be, for example, sheet metal or other material capable ofslight deflection in order to enter the tank 10. The strip is driventhrough the tank 10 by a pair of rollers 14 and 15.

Contained within the tank is a secondary or cleaning enclosure 16 madeup of a pair of converging rigid side walls 17 and 20. For ease ofmanufacture, the rigid side walls 17 and 20 are made up of comparativelyheavy steel plate, 1%" in thickness, backed by a crosswork of stiifeningribs 21 and 22. This arrangement is desirable since, in sonic cleaningemploying the frequency range of 100 to 30,000 cycles per second with apreferred operating frequency of 10,000 cycles per second, in order forthe side walls of the internal enclosure to react as rigid members atsuch an operating frequency, they should have an equivalent thickness ofapproximately two inches; that is, in excess of one-tenth of thewavelength of the radiated energy. This equivalent thickness is obtainedby means of stiifeners 21 and 22.

At the upper convergent region of the side walls 17 and 13 are a pair ofelongated slots 19 and 20 for introducing the strip material 13 into theinner enclosure 16. The side walls have extensions 23 and 24 for guidingthe strip material 13 into the chamber 16, which chamber extends abovethe level of the slots 19 and 20 a distance of one-half wavelength ofthe sonic cleaning energy. The upper end of the inner chamber 16 in theembodiment of FIG. l is open to the air. A source of cleaning liquidwhich may simply be a water pump 2S, as shown in the drawing, delivers aflow of liquid into the chamber 16 through an inlet pipe 26 so as tomaintain the chamber 16 full at all times. Excess liquid spills over thesides of the cleaning enclosure 16 into the tank 10 proper, maintaininga constant level within the inner enclosure 16.

The lower end of the inner chamber is closed by a curved wall member 2.7in the form of a section of a cylinder mounting a plurality oftransducers 28 with their working faces 29 within the inner enclosure 16and their driving elements 30 outside of the tank 10. Althoughtransducers of various types are satisfactory for use in this apparatus,the magnetostrictive transducer and mounting arrangement preferred asdisclosed in Patent No. 2,- 864,592 to L. W. Camp, issued December 16,1958. The transducers 28 are energized from an electrical generator 31of suitable frequency.

Examining now in more detail the enclosure 16 in which the sonictreatment or cleaning takes place, it may be seen that the array oftransducers 28 in the lower cylindrical wall 27 are directed so as tofocus the sonic energy produced in approximately the region beyond theend of the side walls 17 and 18. As indicated in the drawing by theletter P0, a surface of highest pressure variation exists directly atthe faces 29 of the transducers 28. The chamber 16 is approximately twoand one-half wave lengths high from the face 29 of the transducers 28 tothe upper free surface 32 of the cleaning liquid. The free surface 32constitutes a boundary between the liquid medium within the enclosure 16and the ambient air. The impedances of the two media differ by a factorof about 3,600 to 1, so the boundary constitutes a useful reflector forthe sonic energy radiated toward the surface 32. With the side walls 17and 18 rigid at the frequency of sonic energy within the enclosure 16,little or none of the energy is transmitted to the outer tank 10. Thechamber 16 including the transducer faces 29 as sources of sonic energyat the lower end of the rigid side walls 17 and 18, along with thereflective surface 32, causes the establishment of a standing wavepattern as indicated in the drawing. Above the first region of maximumpressure variation P0 adjacent to the faces 29 of the transducers 23 isa region of maximum velocity V, at a half wavelength distance from thetransducer faces, and two other levels of maximum pressure variationlabeled P1 and P2 at one and two wavelengths, respectively, from thefaces 2S. It should be noted that the material to be treated, strip 13,is positioned at two wavelengths distance from the faces 29 of thetransducers 28. At this point the converging or focusing effect of thearray in combination with the side walls exceeds the attenuation of theenergy passing through the medium; therefore, high intensity sonicpressure changes sufiicient to produce cavitation exist over the area ofthe strip 13 within the enclosure 16. The material being relatively thincompared with the wavelength, c g., six inches, of the sonic energy inthe medium allows the transmission of the energy through the strip 13into the liquid contained above and within the enclosure 16. The freesurface 32 at the upper end of the enclosure positioned at a pressurenode (and a velocity anti-node) labeled V, reflects the transmittedenergy back to produce the standing wave pattern as previouslyindicated.

Referring to FIG. 2, at the distance two wavelengths from the transducerfaces 29 is the elongated slot 19 through which passes the strip ofmaterial 13 to be treated. The strip 13 passes into the slot 19 afterriding over a roller 14 which is journaled in bearings 31 and 32 to bedriven by power applied to a pulley 33.

In the plane of FIG. 2, the transducers 28 are arranged with theirworking faces 29 parallel to the strip 13 so that their energy isequally distributed over the entire width of the strip 13 passingthrough the tank. The inner chamber 16 of the tank 10 in which thetreatment or cleaning takes place is actually shaped like a sector of acylinder with the faces 29 of the transducers 20 forming a major part ofthe outer curved wall. The end walls 36 and 37 of the inner chamber 16are subject to sonic energy and, therefore, are of re-enforced designsimilar to the side walls 17 and 18 of enclosure 16 in order to achievean effective thickness in excess of two inches.

The embodiment of FIG. l and FIG. 2 is adapted for the sonic treatmentof semirigid materials, such as sheet metal. One particular usefulapplication is in the removal from plate glass of plaster of Parisadhering there to from the bed used to support the glass in the grindingstep of manufacture.

The plaster of Paris is Va particularly tenacious material and must beremoved from each side after grinding. The plate glass may be in theorder of inches wide, one-half inch in thickness, and continuouslengths. Plate glass, being a relatively rigid material, is not capableof bending enough to enter the cleaning tank as shown in FIG. 1.Therefore, an arrangement is required in which the strip does not haveto bend. Such an arrangement is shown in FIG. 3, in which the cleaningchamber 16 is positioned with the slots 19 at transport table height forthe passage of the rigid strip 13 through the chamber 16. Because of theproblem of constant loss of cleaning liquid and since the enclosure isnot immersed in a surrounding tank, the cleaning enclosure is closed inits upper end in contrast with the embodiment of FIG. l and FIG. 2. Thisapparatus is identical with that of FIG. 1 and FIG. 2 in most otherrespects, and the same reference numerals are used when the elements areidentical. It employs a pair of converging side walls 17 and 18 definingchamber 16. The divergent end of the chamber 16, as in FIG. .1 and notshown in FIG. 3, is closed by a sheet metal member and mounts an arrayof transducers. In the upper region of the chamber 16 at a distance twowavelengths from the faces of the transducers are a pair of extensions23 `and Z4 defining slots 19 and 20 for allowing the passage of thestrip material 13 lto be cleaned through the cleaning chamber 16. Abovethe slot 1S and 19 level, at one-half wavelength distance, is an upperclosure in the form of a thin diaphragm 40 which may be planar or may beslightly concave to conform to the standing wave pattern within thechamber 16. A positive pressure of liquid within the chamber ismaintained in the same manner as in FIG. 1 by a pump. This source forliquid will compensate of the loss of liquid owing to escape through theslots 18 and 19, in particular the outlet slot 19.

The upper closure or diaphragm '40 maintains a constant, smoothreflecting surface for sonic energy within the chamber 16. No turbulenceat the surface, as may be encountered in the embodiment of FIG. l, ispresent since the liquid is restrained within the chamber 16 by thediaphragm 40. 'I'he acoustic impedance mismatch between the liquidmedium in the chamber and the air without still exists so that theboundary provides etticient reflection of energy back into the chamberand toward the strip to be cleaned. The closure 40 forming the boundaryfor reflection is positioned at one-half wavelength beyond the strip 13,so that reflected energy reaching the strip 13, after striking theboundary, will again be at a pressure anti-node -to reinforce the directenergy vat the strip 13.

Another embodiment of this invention employing a rigid upper closure Silmay be seen in FIG. 4. In this embodiment, the closure 50 is positioneddirectly above the strip material 13 to be cleaned. In this case theclosure 50 is a rigid reflector of the same general nature as the sidewalls. Reflection is thereby accomplished not by the liquid-airboundary, but by a liquidsolid boundary. In order to obtainreinforcement, the rigid closure is positioned directly, or as nearly aspossible, -at a pressure anti-node; in other words, at an incrementalwavelength distance from the transducers. In the embodiment of FIG. 4the rigid reflector 50 is positioned directly in contact with the stripto be cleaned.

In all the embodiments of this invention, sonic treatment isaccomplished in a chamber so arranged to provide focusing of sonicenergy from remote transducers with openings arranged to pass thematerial lto be treated through the chamber. The openings are at apredetermined distance from the working faces of the transducers. Asshown, this distance is two wavelengths at the operating frequency ofthe transducers. Of course, with proper proportioning of the walls ofthe chamber, this distance may be one, two, three, or any integralwavelength distance. In addition to the effect achieved by focusing, thechamber is designed to enhance the cleaning effect owing to energyreflected from the end of the converging chamber back to the work piece,or strip. The reflecting surface may be the boundary between the liquidcontained within the chamber and air, and in these circumstances theboundary would be at a half-wavelength distance beyond the work piece.The reflecting surface, alternatively, may be the air-solid boundary atthe outside of a thin metal skin 40 as shown in FIG. 3. That reflectingboundary should also be placed at a wavelength distance beyond theworkpiece. A liquid-solid boundary 50 as shown in FIG. 4, however,should be positioned directly on the Work piece. Employing the conceptof this invention, improved cleaning of strip material is readilyachieved without the problem of undue wear because of cavitation at thefaces of the transducers.

Although for the purpose of explaining the invention va particularembodiment thereof has been shown and described, obvious modicationswill occur vto a person skilled in the art, and I do not desire to belimited to the exact details shown and described.

Iclaim:

1. Sonic treating apparatus comprising:

a chamber including rigid converging side walls;

a curvilinear end wall at the divergent end of Ithe chamber;

a plurality of transducers mounted in the end wall with radiatingelements directed to introduce sonic vibrations into the chamber towarda common focus beyond the convergent end of the chamber;

the convergent end of the chamber positioned at an odd multiple ofhalf-wavelengths of the acoustic energy radiated by the transducers intothe chamber;

and means for positioning articles to be treated within the chamber atsubstantially a point an incremental wavelength distance from theradiating surfaces of the transducers.

2. Sonic treating apparatus comprising:

a chamber including rigid converging side walls;

a curvilinear end wall at the divergent end of the side walls;

a plurality of transducers mounted in the end wall with radiatingelements directed to introduce vibrations into the chamber;

the convergent end of the chamber defining a reflecting boundary of theliquid within the chamber;

the reflecting boundary being at an odd multiple of half-wavelengths ofthe energy radiated by the transducers;

the side walls of the` chamber including restricted openings forintroducing material to be treated through the chamber;

the restricted openings being positioned to introduce the material at apoint substantially an incremental wavelength from the radiatingsurfaces of the transducers.

3. Sonic treating `apparatus comprising:

a chamber including rigid converging side walls;

a curvilinear end wall at the divergent end of the side walls;

a plurality of transducers mounted in the end wall with radiatingelements directed to introduce sonic energy into the chamber;

a closure at the convergent end `of the chamber constituting areiiecting surface for sonic energy directed thereagainst;

the walls of said convergent chamber including aligned openings at anincremental wavelength distance from the radiating elements of saidtransducers for the passage of continuous strip materials through thetreating apparatus.

4. Sonic treating apparatus comprising:

a chamber including rigid converging sidewalls;

a curvilinear end wall at the divergent end of the sidewalls;

a plurality of transducers mounted in the end wall with radiatingelements directed to introduce sonic energy into the chamber;

a closure at the convergent end of the chamber constituting a reflectingsurface for sonic energy directed thereagainst;

said closure constituting a thin diaphragm exposed on one face to theliquid medium within the chamber and on the opposite face to air;

and means positioning articles to be treated in the chamber atsubstantially an incremental wavelength distance from the radiatingsurfaces of the transducers.

5. The combination in accordance with claim 4 wherein said diaphragmclosure is positioned at an odd multiple of half-wavelengths of theenergy introduced into the chamber bythe transducer.

6. Sonic treating apparatus comprising:

a chamber including converging rigid sidewalls;

a plurality of transducers positioned to radiate sonic energy into saidchamber in the direction of convergence Iand toward a common focusbeyond the convergent end of said chambers;

said sidewalls including restricted openings at integral wavelengthdistance therealong from said transducers for passing continuous stripsof material to be treated through said chamber in a direction generallytransverse to the direction of propagation of energy within saidchamber;

and means'including a closure at the convergent end of said chambermaintaining 'a liquid medium within said chamber at least between saidtransducers and said material to be treated.

7. The combination in accordance with claim 6 wherein the closure forthe convergent end of the chamber comprises a rigid reflective surface.

8. The combination in accordance with claim 6 wherein said closure ispositioned at an incremental wavelength distance from the radiatingsurfaces of the transducers.

9. Sonic treating apparatus comprising:

a chamber;

an array of transducers mounted within said chamber with radiatingelements directed to introduce vibrations into the chamber toward acommon focus at a point outside of a boundary of the chamber, theboundary of the chamber between the transducers and focus defining areecting boundary of liquid medium within the chamber;

the reflecting boundary being in an odd multiple of half wavelengths ofthe energy radiated by the transducers;

said chamber including restricted openings for introducing material tobe treated through the chamber;

the restricted openings being'positioned to allow the introduction ofmaterial in a direction generally transverse to the direction ofradiation of sonic energy and at a point substantially an incrementalwavelength distance from the radiating surfaces of the transducers.

l0. Sonic treating apparatus comprising:

a chamber including converging rigid side walls;

a plurality of transducers positioned to radiate sonic energy into saidchamber in the direction of convergence and toward a common focus beyondthe convergent end of said chamber;

a sonic energy-reflecting boundary positioned at an odd number of halfwavelengths from the working surfaces of said transducers;

and means for passing material to be treated through said chamber atsubstantially 4an incremental wavelength distance from the operatingsurface of said transducers and means maintaining a liquid medium withinsaid chamber between said transducers and said material to be treatedand between said material and the convergent end wall of the chamber;

whereby sonic energy passing through the material treated is reflectedinto the chamber to reinforce the directly propagated sonic energy.

References Cited in the le of this patent UNITED STATES PATENTS2,484,014 Peterson Oct. l1, 1949 2,522,071 Tait Sept. l2, 1950 2,632,634Williams Mar. 24, 11953 2,950,725 Jacke Aug. 30, 1960 2,987,068 BransonJune 6, 19611

